A basic heat pipe comprises a closed or sealed envelope or a chamber containing an isotropic liquid-transporting wick and a working fluid capable of having both a liquid phase and a vapor phase within a desired range of operating temperatures. When one portion of the chamber is exposed to a relatively high temperature it functions as an evaporator section. The working fluid is vaporized in the evaporator section causing a slight pressure increase forcing the vapor to a relatively lower temperature section of the chamber defined as a condenser section. The vapor is condensed in the condenser section and returned through the liquid-transporting wick to the evaporator section by capillary pumping action.
Because it operates on the principle of phase changes rather than on the principles of conduction or convection, a heat pipe is theoretically capable of transferring heat at a much higher rate than conventional heat transfer systems. Nevertheless a number of difficulties have been experienced in attempting to use heat pipes for certain applications. material such as a fine-pore wire mesh, the rate of fluid mass flow and consequently heat transfer is limited due to the high pressure drop encountered by the fluid as it flows through the wire mesh. To eliminate this pressure drop, permit increased fluid flow rates and increase heat transfer rates or heat transport capacities, pedestal-artery type heat pipes have been fashioned.
In a pedestal-artery type heat pipe, a fluid-conducting wire mesh artery is supported by a wire mesh stem in fluid communication with a wicking medium or fine circumferential grooves disposed on the inner periphery of the heat pipe wall. The fluid-conducting artery is generally designed to promote automatic priming or filling. Once filled, the artery characteristically has a pressure drop equivalent to a round tube allowing relatively high heat transport capacities.
In the absence of gravity (e.g., in space), any size artery of this type can theoretically prime. However, most heat pipes suitable for use in space applications must pass a ground (gravity) test before the heat pipe can be used. In the presence of gravity, artery priming is governed by design factors limiting heat pipe transport capacities to only thousands of watt-inches (heat transport rate times distance). However, analysts have estimated that future heat pipe transport capacities in the range of millions of watt-inches may be required thereby necessitating a new approach to artery design. Such a new approach is presented in the instant invention.